Optical spectra of the quantum defects in metal halide perovskites

Defects in metal halide perovskites (MHPs) are of fundamental importance to understand optical properties of materials. Here, optical transitions of negative, positive, and neutral defects in MHPs are studied based on the quantum defect model. We find that the intensities of emission peaks are obviously enhanced along with a nonlinear redshift as the depth of defect levels increases in the bandgap. Moreover, the full width at half-maximum of emission spectra can be broadened from tens to hundreds of meV with the increasing temperature. This can be attributed to the strong defect-longitudinal optical phonon coupling, resulting in the enhanced lattice relaxation effect, which could be used as a judging criterion between defects and exciton emission. These results not only provide deep insight for the properties of defect's spectra but also shed light on the influence of defects on the potential applications of MHP-based optoelectronic devices.